Loule, sorry, wrong guess.
Thats a AquaC Urchin, and it does look like its set very low ( the large O-ring around the cup )
It is collecting gunk (the brown stuff) just very few skimmate bubbles.
toy4x4: Have you tried cleaning the injector? (thats the small white screw top that you can see below the skimmer cup.) Maybe its clogged from some detritus or something.
Secondly, do you have the Rio or the Maxi Jet? (or is this a "Pro"?) If you're running the Rio, you should definately upgrade.
Thirdly, have you been cleaning the cup? There could have been something in there thats prohibiting foaming. At least once a week you should rinse it with hot water and wipe it clean with a paper towel or something.
Fourthly, have you been running it with the cover removed, as in the picture? I don't know how much this would affect performance, but you should leave the cover on when running.
Fifthly, have you tried setting the cup very high and see what happens? If its not collecting anything, as it is, that can't do any harm. Raise it almost all the way up and let it run for a couple days. That might be the solution.
Steve